The invention is based on a hydraulic control device for load pressure-Independent control of a double-acting motor.
DE 19 44 822 A1 has disclosed a hydraulic control device for load pressure-independent control of a double-acting motor in which a pressure balance regulator is connected upstream of the metering orifice embodied in the control slide valve element. In this directional-control valve, with the pressure balance regulator connected upstream of the metering orifice, its throttle slide valve element is acted on in the closing direction by the pressure upstream of the metering orifice in the control slide valve element and is acted on in the opening direction by the pressure downstream of the metering orifice, i.e. by the load pressure plus the force of a spring. The pressure balance regulator consequently keeps the pressure difference constant by means of the metering throttle in the directional-control valve even when the load pressure varies and consequently also maintains the associated through flow so that the working speed set in the directional-control valve is kept constant. A directional-control valve of this kind is also referred to as an LS (load sensing) valve with a primary individual pressure balance regulator, which permits a load pressure-independent control. It is disadvantageous that this control device does not permit a supply-dependent oil flow distribution. If directional-control valves of this kind are used to simultaneously control several motors operating in parallel, then first the motor with the lowest load pressure is supplied with a pressure fluid flow while the rest of the volume flow is conveyed to the other motors. The ratio of the distribution of the volume flows, which in this case does not remain constant, changes with the load pressure. Particularly in the event of an undersupply, this can result in the fact that the least loaded motor continues to function while a highly loaded, parallel-actuated motor comes to a standstill, which is undesirable in many applications. Such an LS directional-control valve is relatively complex and expensive; its housing is especially equipped for this design and its components such as the housing, flange patterns, and slide valve are only suited for this LS directional-control valve with a primary individual pressure balance regulator.
Furthermore, such a hydraulic control device for load pressure-compensated control of a double-acting motor is known from DE 36 34 728 A1, wherein two such directional-control valves for a parallel actuation of the associated motors are supplied with pressure fluid by a single variable displacement pump, whose regulator is acted on by the respective maximal load pressure of the two motors by means of a control line containing a series of shuttle valves. In this case, in each directional-control valve, the pressure balance regulator used for load pressure compensation is followed by a metering orifice in the control slide valve element; the pressure balance regulator also precedes the piston sections of the control slide valve element that are used for directional control. The throttle slide valve element in the subsequent pressure balance regulator is acted on in the opening direction by the pressure downstream of the metering orifice and is acted on in the closing direction by the respective highest load pressure and the regulating pressure difference due to the regulating spring. Such directional-control valves with a secondary individual pressure balance regulator, which can also be referred to as LC (load compensating) directional-control valves, permit the disadvantages mentioned at the beginning to be avoided. In this instance, when two or more directional-control valves are operated in parallel and there is not enough pump oil flow, i.e. when there is an undersupply, less oil flows uniformly via all of the metering orifices. The pressure differences in the respective metering orifices are therefore reduced and less oil flows to the motors. The oil flow through the directional-control valves decreases in proportion to the predetermined reference values. In principle, therefore, it involves a valve device for dividing the pump flow into individual partial flows that flow to each motor; even when the motors are placed under different loads, the distribution ratio remains constant and consequently, the motions are maintained without causing the highest loaded motor to come to a standstill. An LC directional-control valve of this kind is also relatively complex and expensive; its housing is especially equipped for this design and therefore has a special housing, flange pattern, and slide valve that are only suited for a directional-control valve with a secondary individual pressure balance regulator.
Furthermore, EP 0 877 169 A2 has disclosed a hydraulic control device for load pressure-independent control of a double-acting motor, which operates with such LC directional-control valves for oil flow distribution in the event of an undersupply and to this end, has secondary individual pressure balance regulators. This directional-control valve also has an additional check valve disposed between the control slide valve element and the pressure balance regulator, which permits higher safety requirements to be met. This directional-control valve also has a housing that is only suitable for an LC type and cannot be used in an LS directional-control valve with a primary individual pressure balance regulator.